1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to bonding between a power semiconductor element and a metal plate in the semiconductor device.
2. Description of the Background Art
A power semiconductor element in a semiconductor device controls an amount of a current flowing between a front surface and a back surface thereof, and heat is generated due to power loss in a case where the current flows. For this reason, the power semiconductor element is connected to a metal conductor used for conduction as well as heat dissipation with the use of a bonding material (bonding member) such as solder, to thereby perform electrical connection with the outside and heat dissipation.
In a case where a power semiconductor element itself is increased in size for controlling a large current, and the thickness of a heat sink is increased for improving heat dissipation properties of the heat generated as a result of this, there is a fear that a difference in coefficient of linear expansion between a metal conductor and a power semiconductor element may cause distortions in the power semiconductor element, which may break the semiconductor element.
In order to prevent the power semiconductor element from being broken, it is required to increase the thickness of a bonding member that connects a metal conductor and a power semiconductor element, but the solder used as the bonding member has lower heat conductivity and conductivity than those of the metal conductor, leading to a problem that heat dissipation properties as well as electrical resistance are deteriorated.
As the method of solving the above-mentioned problem, Japanese Patent Application Laid-Open No. 55-93230 and Japanese Patent Application Laid-Open No. 62-198140 describe the method of disposing a mesh metal body between a power semiconductor element and a metal conductor, to thereby bond the power semiconductor element to the metal conductor while immersing a bonding member (for example, solder) for bonding them.
However, even the methods described in Japanese Patent Application Laid-Open No. 55-93230 and Japanese Patent Application Laid-Open No. 62-198140 have a problem that heat dissipation properties are deteriorated in a case where the thickness of the bonding member is increased for controlling a much larger current.